Use of a tetraphenylphosphonium halogenated salt as smoke-producing agent and smoke-producing pyrotechnic composition incorporating such a material

ABSTRACT

Disclosed is the use of at least one tetraphenylphosphonium halogenated salt as smoke-producing agent in a pyrotechnic composition designed to ensure masking of a target with regard to electromagnetic radiation in a given wavelengths range. Also disclosed is also a smoke-producing pyrotechnic composition including at least one tetraphenylphosphonium halogenated salt.

BACKGROUND OF THE INVENTION Field of the Invention

The technical field of the invention relates to smoke-producing pyrotechnic compositions and, more specifically, smoke-producing compositions that are able to mask a target with regard to electromagnetic radiation in a given wavelengths range.

Description of the Related Art

Research is being carried out nowadays to find smoke-producing agents that are able to cover a broad spectrum of wavelengths, ranging from the visible to the far infrared spectrum, that is to say wavelengths from 0.7 micrometers to 14 micrometers.

From patents FR2583037 and FR2560186 compositions are known that associate an oxidant, a reductant and a material able to generate masking particles consisting of a chlorinated aromatic compound. The masking particles thus generated are essentially carbon particles with an average granulometry close to the wavelengths of the radiation which is to be concealed.

These compositions are very effective from a masking point of view, both with regard to the visible spectrum and the infrared fields: range of 3 to 5 micrometers and range of 8 to 12 micrometers. However, they have the disadvantage that they use a substance, chlorinated naphthalene, which is now banned from manufacture and use by the European Union.

There is thus a need to devise, for the protection of land and naval forces, new pyrotechnic masking compositions that are able to mask a broad spectral field using low-toxicity components.

From patent WO2015/132266 a smoke-producing composition is also known in which the material generating masking particles consists of a polyaromatic compound substituted by 1 to 3 atoms of bromine, such as a dibromonaphthalene or a dibromoquinoline, and more specifically 1,4-dibromonaphtalene, 1,8-dibromoquinoline or 4,7-dibromoquinoline.

This composition thus allows, by replacing chlorine with bromine, for the creation of a smoke-producing composition with substantially the performance of the known one, based on chlorinated naphthalene, while being less toxic than the latter.

SUMMARY OF THE INVENTION

The purpose of the invention is to propose a new smoke-producing composition which is less toxic but has a certain masking effectiveness, both in the visible and the infrared range.

The purpose of the invention is thus the use of at least one tetraphenylphosphonium halogenated salt as smoke-producing agent in a pyrotechnic composition designed to ensure masking of a target with regard to electromagnetic radiation in a given wavelengths range.

These halogenated salts are commercially available and listed under international CAS numbers:

2751 90 8 for tetraphenylphosphonium bromide;

2001 45 8 for tetraphenylphosphonium chloride;

2065 67 0 for tetraphenylphosphonium iodide;

3587 05 1 for tetraphenylphosphanium fluoride.

To date, they have never been used in pyrotechnic compositions, whether smoke-producing or not.

They are most often used as precursors or intermediates in the synthesis of other compounds, particularly in the pharmaceutical field. As a matter of fact, their structure facilitates the precipitation of organic molecules.

The applicant discovered that the combustion of these salts led to the formation of mainly phosphonic acid and not phosphoric acid, as is the case with most known organophosphoruses.

This phosphonic acid is much less toxic than phosphoric acid and leads to masking clouds with reduced toxicity.

Furthermore, this combustion of organophosphoruses leads to the formation of highly efficient masking clouds with regard to infrared radiation.

A tetraphenylphosphonium halogenated salt has the following structural formula in which X⁻ designates the halogen ion (chlorine, bromine, iodine or fluorine).

This molecule has four aromatic cycles which, during combustion, ensure the production of the desired carbon particles for masking.

Combustion will lead to the recombination of the halogen atoms with the other species: carbon or hydrogen, resulting in hydrogen halides or halogenated carbon derivatives.

Phosphorus recombines as phosphonic acid.

The tetraphenylphosphonium salt preferably used is tetraphenylphosphonium bromide.

This salt is low-cost and, as described in patent WO2015/132266, the use of bromine prevents the formation of hydrogen chloride during combustion, which reduces the toxicity of the fumes.

It would also be possible to use the other halogenated salts that will ensure comparable masking performances. However, tetraphenylphosphonium bromide or tetraphenylphosphonium iodide is preferable to reduce the toxicity of the generated cloud.

The object of the invention is also a smoke-producing pyrotechnic composition designed to mask a target with regard to electromagnetic radiation in a given wavelengths range and comprising at least one energetic material, such as a reduction-oxidation couple, as well as at least one smoke-producing agent generating masking particles, the composition being characterised in that it comprises as smoke-producing agent at least one tetraphenylphosphonium halogenated salt.

An energetic material is a material or composition which can be initiated and which provides sufficient energy to burn the smoke-producing agent and thus cause the emission of masking particles, mainly carbon particles. Combustion shall be conducted at sufficient power to avoid extinction of the smoke-producing mass.

As energetic material a reduction-oxidation couple can be used, for example a couple associating, as a reductant, a metallic powder and, as an oxidant, a fluoropolymer having in its molecular structure a fluorine percentage above 60%.

The reductant may be selected from among the following bodies: aluminium, zirconium, magnesium, titanium, calcium silicide, boron.

The oxidant may be selected from among the following bodies: vinylidene fluoride and hexafluoropropylene dipolymer (for example, the product marketed by the company 3M under the brand name Dyneon FC2230), polytetrafluoroethylene, tetrafluoroethylene or their mixtures.

According to a particular embodiment, the composition can comprise: at least one organochlorinated compound in a proportion below 10% in mass. This chlorinated compound allows for the generated smoke to be better maintained on the ground.

As a matter of fact, the chlorine will combine during combustion with the carbon species of the cloud, forming molecules of relatively high molecular mass, this recombination will have a mechanical effect of increasing the weight of the cloud.

It has the advantage of increasing the duration of outdoor masking for a given mass of composition by avoiding that the smoke disperses too rapidly.

This chlorinated compound will be added in a small proportion so as not to excessively increase the toxicity of the cloud. A body incorporating a large number of chlorine atoms will be selected (chlorination rate above 60%) so that, despite the reduced mass, the chlorine recombination has a significant effect.

For example, one can use the compound marketed under the brand name Dechlorane plus by the American company Oxychem. This compound is a polyheteroaromatic used as a well-known flame-retardant and is listed under CAS number 13560-89-9. It contains 12 chlorine atoms in its molecular structure.

More precisely, the masking composition according to the invention can associate:

-   -   from 10 to 40% in mass of energetic material and preferably 20%         to 30%,     -   from 90% to 60% in mass of smoke-producing agent and preferably         60% to 70%,     -   from 0% to 10% in mass of chlorinated agent and preferably 0 to         7%,     -   from 0% to 8% in mass of binding agent and preferably 0 to 5%.

The binding agent allows for improvement of the mechanical strength of the block of composition which will be created, for example, by compression.

The binding agent may consist of at least one epoxy-type resin added in a proportion of approximately 5% of the overall mass of the bloc (for a bloc of 100 grammes, 5 grammes of binding agent are added).

In all cases, compression will be carried out at a relatively high compression rate (for example, 17 mega Pascals for a diameter of 125 mm).

BRIEF DESCRIPTION OF THE DRAWINGS

With the intention of better showing the characteristics of the invention, some examples of compositions according to the invention and their use are described hereinafter, by way of an example without any limiting nature, with reference to the accompanying drawings wherein:

FIG. 1 is a curve showing the evolution over time of the camouflage coefficient Cm for a composition according to example 2 hereunder;

FIG. 2 shows the evolution over time of the camouflage coefficient Cm for a composition according to example 3 hereunder;

FIG. 3 shows the evolution over time of the camouflage coefficient Cm for a composition according to example 4 hereunder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The applicant has created a certain number of compositions according to the invention (proportions of the constituents provided in relation to the total mass of the composition) and has evaluated their masking performances.

EXAMPLE 1

-   -   12% in mass of magnesium powder,     -   18% in mass of vinylidene fluoride and hexafluoropropylene         dipolymer,     -   63% in mass of tetraphenylphosphonium salt,     -   7% in mass of chlorinated agent.

This composition is formed into a block without binding agent. The bloc is created by compression at the compression rate specified above (17 mega Pascals for a diameter of 125 mm). Such compression rate is sufficient to ensure the cohesion of the block.

EXAMPLE 2

-   -   12% in mass of magnesium powder,     -   12% in mass of vinylidene fluoride and hexafluoropropylene         dipolymer,     -   69% in mass of tetraphenylphosphonium salt,     -   7% in mass of chlorinated agent,     -   5% in mass of epoxy resin.

EXAMPLE 3

-   -   15% in mass of magnesium powder,     -   15% in mass of vinylidene fluoride and hexafluoropropylene         dipolymer,     -   69% in mass of tetraphenylphosphonium salt,     -   5% in mass of epoxy resin.

EXAMPLE 4

-   -   15% in mass of magnesium powder,     -   15% in mass of vinylidene fluoride and hexafluoropropylene         dipolymer,     -   62% in mass of tetraphenylphosphonium salt,     -   7% in mass of chlorinated agent,     -   5% in mass of epoxy resin.

For each composition a smoke-producing block of approximately 800 grammes was created.

This block was positioned in an optronic tunnel at a distance of 6 meters from the optical measurement line.

The combustion of the block occurs in the manner of a “cigarette”. Initiation thus happens at the level of the free upper surface of the bloc which is gradually consumed from its upper surface to its lower surface (bearing surface).

The generated smoke cloud was displaced by a fan at a controlled speed of 3 m/s in such a way as to make it pass in front of the means of measurement.

The means of measurement include:

-   -   a hot source that has a regulated temperature of around 160° C.;     -   a cold source (consisting of the steel wall of the optronic         tunnel);     -   a thermal camera observing in band 3 (spectral window of 8 to 12         μm).

Masking is evaluated by comparing the effect of the smoke passing in front of the thermal sources (cold and hot) on the temperature seen by the thermal camera.

For each batch tested, the camouflage coefficients Cm (in percentage points) are calculated by applying the following formula:

${C_{m}(t)} = {100 \times \left( {1 - \frac{\left( {{{Nb}(t)} - {{Nn}(t)}} \right)}{\left( {{Nb}^{\prime} - {Nn}^{\prime}} \right)}} \right)}$

Formula in which:

-   -   Nb(t) and Nb′ are the numerical levels measured by the camera at         the hot source, with smoke (Nb(t)) and without smoke (Nb′);     -   Nn(t) and Nn′ are the numerical levels measured by the camera at         the cold source, with smoke (Nn(t)) and without smoke (Nn′).

As stated above, the annexed figures show the evolution over time on the x-axis and the camouflage coefficient Cm on the Y-axis for different examples of compositions.

FIG. 1 corresponds to the composition according to example 2, FIG. 2 corresponds to the composition according to example 3 and FIG. 3 corresponds to the composition according to example 4.

When considering all the figures, it is noticeable that the masking compositions according to the invention provide a camouflage coefficient above 45% for a duration of at least 90 seconds, which is particularly advantageous.

Furthermore, the masking performances are very similar for the different compositions, which indicates a certain operational stability even with a few % of formulation deviations.

It is also noticeable that the smoke-screen deploys quickly. It takes between 3 seconds and 10 seconds.

It was also noted, in other tests, that the rate of combustion depends on the magnesium content. Thus, the rate of combustion increases as the magnesium content increases. For example, a magnesium content of 15% provides a combustion duration for the bloc of nearly 52 seconds, whilst a magnesium content of 12% provides a combustion duration of 88 seconds.

This is not particularly visible on the figures that show the results of firing tunnel tests.

Moreover, it was observed that adding Dechlorane increased the masking duration in the case of outdoor combustion.

It is obvious that the invention is by no means limited to the examples described above, but that numerous modifications can be made to the smoke-producing pyrotechnic composition and its use described above, without departing from the scope of the invention as defined in the following claims. 

1. A method to mask a target with regard to electromagnetic radiation in a given wavelengths range, comprising providing a pyrotechnic composition comprising at least one tetraphenylphosphonium halogenated salt as a smoke-producing agent, and applying the composition to mask the target.
 2. The method according to claim 1, wherein the tetraphenylphosphonium halogenated salt used is tetraphenylphosphonium bromide.
 3. The method according to claim 1 in order to obtain masking with a camouflage coefficient above 45% for a duration of at least 90 seconds.
 4. Smoke-producing pyrotechnic composition intended to mask a target with regard to electromagnetic radiation in a given wavelengths range and comprising at least one energetic material, such as a reduction-oxidation couple, as well as at least one smoke-producing agent generating masking particles, the composition comprising as smoke-producing agent at least one tetraphenylphosphonium halogenated salt.
 5. The composition according to claim 4, comprising as smoke-producing agent tetraphenylphosphonium bromide or tetraphenylphosphonium iodide.
 6. The composition according to claim 5, comprising as energetic material a reduction-oxidation couple associating, as a reductant, a metallic powder and, as an oxidant, a fluoropolymer.
 7. The composition according to claim 6, wherein the fluoropolymer is a fluoropolymer having in its molecular structure a fluorine percentage above 60%.
 8. The composition according to claim 6, comprising at least one reductant selected from among the following bodies: magnesium, aluminium, zirconium, titanium, calcium silicide, boron.
 9. The composition according to claim 6, comprising at least one oxidant selected from among the following bodies: vinylidene fluoride and hexafluoropropylene dipolymer, polytetrafluoroethylene, tetrafluoroethylene or their mixtures.
 10. The composition according to claim 6, comprising at least one chlorinated compound in a proportion below 10% in mass.
 11. The composition according to claim 10, comprising at least one organochlorinated compound with a chlorination rate above 60%.
 12. The composition according to claim 4, comprising: 10% to 40% in mass of energetic material, 90% to 60% in mass of smoke-producing agent, 0% to 10% in mass of chlorinated agent, 0% to 8% in mass of binding agent.
 13. The composition according to claim 12, wherein the binding agent consists of at least one epoxy-type resin added in a proportion of approximately 5% of the overall mass of the bloc.
 14. The composition according to claim 12, comprising: 12% in mass of magnesium powder, 18% in mass of vinylidene fluoride and hexafluoropropylene dipolymer, 63% in mass of tetraphenylphosphonium salt, 7% in mass of chlorinated agent.
 15. The composition according to claim 12, comprising: 12% in mass of magnesium powder, 12% in mass of vinylidene fluoride and hexafluoropropylene dipolymer, 69% in mass of tetraphenylphosphonium salt, 7% in mass of chlorinated agent, 5% in mass of epoxy resin.
 16. The composition according to claim 12, comprising: 15% in mass of magnesium powder, 15% in mass of vinylidene fluoride and hexafluoropropylene dipolymer, 69% in mass of tetraphenylphosphonium salt, 5% in mass of epoxy resin.
 17. The composition according to claim 12, comprising: 15% in mass of magnesium powder, 15% in mass of vinylidene fluoride and hexafluoropropylene dipolymer, 62% in mass of tetraphenylphosphonium salt, 7% in mass of chlorinated agent, 5% in mass of epoxy resin.
 18. The composition of claim 12, wherein the mass of the energetic material is 20% to 30%.
 19. The composition of claim 18, wherein the mass of the smoke-producing agent is 60% to 70%.
 20. The composition of claim 19, wherein the mass of the chlorinated agent is 0 to 7%. 